| Title | Modelling Thermal Response and Tracer Tests in a Complex Fractured Aquifer System |
|---|---|
| Authors | Meissam L. Bahlali, Carl Jacquemyn, Matthew Jackson, Adrian Butler, Joseph Kelly, Fleur Loveridge, Dave |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | |
| Abstract | The Chalk aquifer supports over 50 open-loop shallow geothermal systems across southern and eastern UK. However, the behaviour of thermal plumes and the impact on energy production and recovery efficiency remain poorly understood. The aquifer has a complex dual-porosity structure with high-permeability zones, created by fracturing and/or karstification, embedded within a low-permeability matrix. Groundwater flow varies significantly across these zones, creating complex thermal plume geometries and increasing risks of thermal interference between wells. We present numerical modelling of a Thermal Response Test (TRT) and an Open Loop Thermal Tracer Test (OL-TTT) conducted in the same Chalk borehole in Berkshire, UK. Extensive monitoring included distributed temperature sensors, electrical resistivity tomography, and seismic monitoring to capture plume evolution and aquifer heterogeneity. The OL-TTT aimed to image the evolving thermal plume around the injection borehole and assess the impact of heterogeneity. A TRT in the same borehole was undertaken earlier. Our numerical simulations of the OL-TTT show heat is transported rapidly from the injection borehole towards the abstraction well through several high-permeability fracture zones. The model includes an adjustable effective rock thermal capacity; when low, it approximates a scenario where the rock matrix does not thermally equilibrate with warm groundwater in fractures, resulting in small thermal retardation. These results suggest that models assuming thermal equilibrium may underestimate heat transport distances and associated risks of thermal interference and breakthrough. Numerical modelling of the earlier TRT is currently ongoing. |